What does this do?

[LL]

#include <stdio.h>

int main() {
enum {
TEST1, TEST2
} stuff_to_print;

printf(TEST1, TEST2); // what does this do? Gives no output.
}

 

[Keith Thompson]

#include <stdio.h>

int main() {
enum {
TEST1, TEST2
} stuff_to_print;

printf(TEST1, TEST2); // what does this do? Gives no output.
}

It invokes undefined behavior.

Where did you find that horrid piece of code?

 

[CBFalconer]

It invokes undefined behavior.

Where did you find that horrid piece of code?

Is it undefined? Is it equivalent to "printf(0, 1);"? Is that
equivalent to "printf(NULL, 1);"? Is that undefined behaviour?

 

[Ben Pfaff]

Is it undefined? Is it equivalent to "printf(0, 1);"? Is that
equivalent to "printf(NULL, 1);"? Is that undefined behaviour?

Yes, yes, yes, and yes.

 

[Keith Thompson]

Ben Pfaff said:


In which order?

Normally either 1,2,3,4 or 4,3,2,1, but it's 2,1,4,3 on a PDP-11.

 

[Phil Carmody]

Ben Pfaff said:


In which order?

This is one of the times where the ',' induces a sequence point.

Phil